Phase-change inks are desirable for ink-jet printers because they remain in a solid phase at room temperature during shipping, long-term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink-jet inks are largely eliminated, thereby improving the reliability of the ink-jet printing. Further, in phase-change ink-jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Phase-change or “hot-melt” inks typically used with ink-jet printers have a wax-based ink vehicle, e.g., a crystalline wax. Such solid ink-jet inks provide vivid color images. In typical systems, these crystalline-wax inks partially cool on an intermediate-transfer member and are then pressed into the image-receiving medium such as paper. Transfuse spreads the image droplet, providing a richer color and lower pile height. The low flow of the solid ink also prevents show-through on the paper.
However, the brittle waxes used in inks such as those described above do not provide robust images and are easily scratched. Low-viscosity inks, such as those curable by ultraviolet (UV) radiation, provide one printing option that is both jettable and curable to robust image on paper. These inks lack the thermally driven change in viscosity of hot-melt inks required to successfully transfuse the image as well as prevent image show-through on paper. In addition, UV-curable resin removes the requirement for a hard-wax ink vehicle. The resin can be cured to a tougher material than could ever be found with a wax. However, the transfuse drum makes use of the post-jetting solidification of the wax to preserve dot integrity while the image is built and transferred.
The majority of functionalized materials useful for UV curing are difunctional. Multifunctionality insures that the desired cross-linked network will be achieved. In the dominantly used class, acrylates, three major classes exist: polyethers, polyesters, and polyurethanes, all of which contain oxygen and/or nitrogen in the backbone. Only polyethers prepared from ethylene and propylene glycols have the ability to be of sufficiently low viscosity to be the major component of ink-jettable inks. There are very few long-chain acrylate-mono-functional hydrocarbon monomers and no commercial examples of difunctional acrylates with long hydrocarbon chains. Thus, there remains a need for processes for preparing difunctional acrylates having long hydrocarbon chains.